The present invention relates to a device not only for rounding a belt-like film into a tube along its length direction, but for melding overlapped edges on both sides of said tubular film by ultrasonic vibration in order to form a plurality of packaging bags.
In the conventional device which effects melding of overlapped parts of both side edges of a film rounded to be tubular by heat generated by ultrasonic vibration, as shown in FIG. 7, two overlapping sheets of film 13 are moved in the direction of arrow 14 between a vertically vibrating hammer 10 and an anvil 12 securely held on the frame 11, thereby to continuously meld the film 13 by vibration heat induced by the hammer. However, because of subtle variations in the thickness of the aforementioned film 13, its melding strength varies from area to area, threatening to cause air leak when vacuum packaging is carried out, for example.
It is therefore an object of this invention to form a tubular film having a uniform strength by averaging the vibratory impact force to be applied onto the film.
The present invention provides a sealing device comprising a means for moving a belt-like film along a tubular plate having both side edges thereof folded to overlap one upon another as if at a kimono""s neck part, thereby to form the film into a continuous tube, following the sectional profile of this tubular plate, wherein an anvil is formed on one end of a spring piece, the other end of which is fixedly set on one side edge of the aforementioned overlapped part of the tubular plate, the overlapped portion of the tubular film may be melded by the cooperation of the aforementioned anvil and a movable hammer which applies an ultrasonic vibratory impact on said anvil.
Further, the present invention provides a sealing device comprising a means for moving a belt-like film along the inner surface of a tubular plate so folded as to form a continuous slit between both side edges thereof, thereby to form said film into a continuous tube, following the sectional profile of this tubular plate, wherein one end of a spring piece is fixedly set to a base block immovably held on one of the sides sandwiching the aforementioned slit, and an anvil is formed on the other end of said spring piece, so that clasped-hands like edges of the tubular film which are thrusted out from the aforementioned anvil may be melded by the cooperation of the aforementioned anvil and a movable hammer which applies ultrasonic vibratory impact on said anvil.